In construction the standard practice when a window or similar element such as a skylight or door is to be mounted between members such as beams, studs, or rafter, is simply to mount a fully prefabricated frame assembly between these members, and to secure it in place by nailing through tabs provided for this purpose. The frame is normally constituted as an annular array of frame elements joined at corners and provided in several standard sizes, as for example a size adapted to fit between a pair of standard studs on 16-inch centers.
A considerable disadvantage of this type of construction is that these frame assemblies must be rather painstakingly packaged and cared for prior to installation. They are relatively bulky so that shipping and storage costs are a problem. What is more it is necessary that the structure in which they are mounted be of predetermined dimensions, as if the opening in which they are to be inserted is off size, filler strips and the like become necessary